I’m pretty new to this game and i would like to ask if it is somehow possible to change monsters in a battle.
Nope. Sorry.
But there will be a monster introduced with a move known as Sendback…so you can just send a bunch of your monsters back if you really, REALLY want a certain monster out…though it really doesn’t matter…
You can get it in eggs ATM. White pony. It’s called Pegasion, and it’s a very strategic 9-star monster. Great against a few powerful strategies.
Or just wait for the other arkadions to get killed.
Monsters…arkadions…Same thing, really. n.n
I didn’t said it was bad:P I just highlighted it 
Suuuure. n.n
You can do it outside of battles you dont have to be in town, just go to your party and use the arrows to move your arks around